It is sometimes desirable to formulate household cleaning and other compositions which under certain conditions of storage or use may generate a gas. For instance, a liquid household cleaning composition including chlorine or oxygen bleach may under some conditions generate a gas. Of course, the generation of any gas in a closed container, especially one which is sealed prior to sale, may make desirable measures to prevent an unanticipated forcible escape of product or gas from the container.
A Vernay Laboratories Inc. Product Brochure copyright 1988 discloses umbrella valves in which the top of the umbrella covers a venting hole.
Pan U.S. Pat. No. 4,210,255 discloses a vent opening closed by a closure held in place by a strip of stretchable material with memory.
Ostrowsky U.S. Pat. No. 4,487,324 discloses a closure including a cylindrical base open at the bottom, an upper wall closing the base at the top, an aperture in the upper wall, a cover hingedly connected to the base with two narrow strips and a wider medial strip, each of the strips having a bend therein, the plug having a plug depending therefrom and accommodated within the aperture when the closure is closed. The cover is biased to two positions, a nearly fully open position and a closed position.
While container closures have been proposed in the past to deal with the problem of over-pressurization, these have not been fully acceptable.